How do substances pass through cell membranes?

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How do substances pass through cell membranes?

Diffusion:

  • from a high to low concentration until equilibrium reached
  • carries hydrophobic (lipid-soluble) or small uncharged molecules
  • through phospholipid bilayer
  • passive, no energy is required

Facilitated diffusion:

  • from a high to low concentration until equilibrium reached
  • hydrophilic molecules or ions
  • through channel proteins or via carrier proteins that change shape
  • passive, no energy required

Active transport

  • against a concentration gradient, from low to high
  • through a carrier protein that changes shape
  • requires energy, ATP 
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How do substances pass through cell membranes?

Osmosis:

  • a type of diffusion involving movement of free water molecules
  • high to low concentration of free water molecules until equilibrium is reached
  • through phospholipid bilayer
  • passive, no energy required

Exocytosis:

  • used for bulk transport of substances out of the cell
  • vesicles fuse with the cell surface membrane, releasing their contents

Endocytosis:

  • used for bulk transport into the cell
  • vesicles are created from the cell surface membrane, bringing their contents into the cell 
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